Tonight's Castle is not an episode to miss. You will love this episode if you have ever watched a sci-fi series (and, if you're a Castle fan who hasn't at least watched Firefly, what's wrong with you?). You will love this episode if you've ever been to a comic or sci-fi convention. You will love this episode if you just enjoy funny, light-hearted Castle episodes.

There really isn't a way to not enjoy "The Final Frontier." And here are five reasons why.

WARNING: There are some pretty big Castle spoilers in this article. None of them should ruin your viewing experience, but you might want to be careful anyway.

In "The Final Frontier," Castle and Beckett find themselves solving a murder that occurs during a sci-fi convention. The organizer of something called the "Nebula 9 Fan Experience" is found dead in her own exhibit and everyone -- from super-fans to washed-up actors -- is a suspect.

Seriously, that description alone should be enough to draw you in. But if it's not, here are five reasons that you really, really have to watch "The Final Frontier."

1. Guest Stars

Castle pulled out all the stops when it came to guest-casting "The Final Frontier." Who do they have? Armin Shimerman (Star Trek: Deep Space 9, Buffy the Vampire Slayer), Ed Quinn (Eureka), Erin Way (Alphas) and Christina Moore (True Blood). In addition to these actors, we also get to see Chris McKenna (an actor who played Joey Buchanan -- just like Nathan Fillion -- on One Life to Live) and the episode's director, Jonathan Frakes (Star Trek: The Next Generation).

2. Geeking Out

Every major Castle character we see in this episode finds something to geek-out about. And then they all make fun of each others' obsessions. Just like a normal Con...

3. A Suitably Sci-Fi Murder Weapon

Even the weaponry in "The Final Frontier" gets in on the action. Remember, people -- always set phasers to stun.

4. Shatner Impressions

What would a sci-fi episode of television be without Captain Kirk impressions? Fortunately, we do not have to find out in "The Final Frontier."

5. Firefly References

Any fan of both Castle and Firefly knows that Nathan Fillion loves to reference his days as Captain Malcolm Reynolds on the sci-fi series. This episode is no exception. Off the top of my head, I can think of at least four obvious references to the one-season, Joss Whedon series. They're shiny.